Japan tests explosion-powered rocket for the first time in space (2021)
autoevolution.com
autoevolution.com
https://www.youtube.com/watch?v=fRMMSyCcTDI
I live vicariously through channels like Integza and Tom Stanton. I've wanted to do some of this stuff for over 20 years, specifically electrohydrodynamic (EHD) engines, but spent nearly the entirety of the last 2 decades merely surviving. It's a strange feeling to watch the world make basically no progress over many years, then suddenly go through an inflection point where suddenly everything is solved and there's no way to catch up. Like with flying cars, reusable rockets, AI..
I dunno, I just feel really inspired, but am also mourning the passing of my own life and all that wasted potential. These are all great inventions, super simple, easy to build, but why the heck were we forced to do everything the hard way for so long and still not make rent? These individual projects are really cool, but I worry that we aren't solving the fundamental problem of underemployment that forces fish to ride bicycles instead of swimming freely. Still just a rat in a cage and all that.
Tell me more about the potential of electrohydrodynamic engines. What excites you there?
I want to know whether it would be possible to efficiently ionize air and push it with electromagnetic pulses. It just seems so futuristic, you know?
https://www.youtube.com/watch?v=nrEBoPYS4ns
Unfortunately, I believe that his design is unlikely to be scalable, since each stage gets less than a linear increase in thrust due to losses. It's like stacking propeller blades. Each stage performs worse as more turbulence is added and the airflow gets less laminar.
IMHO the efficiency comes from the surface area of the anode (the wire). The cathode could be the lifting surface or body of the craft, so isn't that relevant for performance. Foils, pipes, anything works for the cathode. Taken to the limit, the anode might look like a 3D array of point charges, separated by thin insulated wires. Or a mesh with a high surface area to volume ratio. Something that looks more like a big ball of steel wool.
Some experiments have also separated the ionization from the electric field. Like in vacuum tubes, the hot plate can emit electrons regardless of the voltage between anode and cathode. Perhaps a laser could light up the surface of the anode at the exact energy needed to free electrons, I dunno. But I wonder if he's planning to do something similar:
https://www.youtube.com/watch?v=YFkUOPl0tUw
Another problem is that the ions move incredibly fast, potentially faster than the speed of sound, but only drag on the order of 1 in 100 other air molecules with them. It quickly saturates so a linear increase in current gets a sublinear increase in thrust. So an EHD engine is more efficient at lower speed, just like a helicopter prop. That's where creating more ions with more surface area might help. Also pulsed DC might get good airflow with fewer ions, so far the best result I've seen is 886 W/kg, similar to a helicopter:
http://jnaudin.free.fr/html/lftphv.htm
At the end of the day, EHD engines will probably end up working more like drones and balloons than rockets. Although some people have messed with putting the anode in front of a wing for a bit better lift.
Anyway, this is all great and stuff, but people like us on HN are relentless hackers. If I was part of a think tank and found the resources to fund it, I would take these experiments to the limit and build the best possible EHD engine. Maybe try to get to 100 W/kg to start, then shoot for 10, and so on. Which is why I think the Skunk Works or DARPA or someone like that probably built one back in say the 1960s and kept it secret:
https://en.wikipedia.org/wiki/Biefeld–Brown_effect
JP Aerospace was going to build an airship to orbit with their Ascender model, powered by an EHD mesh in front of perhaps an aluminized mylar balloon/cathode:
That's the only real threat to someone like SpaceX that I know of. Their idea could work, although I suspect that thrust reduces proportionately to the air thinning with altitude. So they'll need a way to gather a larger volume of ions in front of the ship, maybe with a laser or something magnetic, as you suggested.
It would be like building an airfoil 100 times more efficient that anything we have now, so that it could fly at 100,000+ feet (20 miles) at 1/100 atmospheres of pressure the way an airplane flies at sea level. Then gradually ascend to perhaps the Karman line at 100 km (60 miles) by changing the geometry of the airship to fly faster or just use rockets like an RDE or something.
Consider writing open proposals. You have a great set of knowledge and ideas. It’s easier than ever to get illustrations that make it seem real. Thanks!
Time waits for no one, from dust we came and to dust we shall go back.
Started building things last year and it’s been a blast (and super frustrating and more expensive than i expected but eh, worth it)
Energy density, ease of transport, robustness, and all sorts of other considerations dominate in an environment that is very hostile. Aside from nuclear power (which we will never get) the future is pretty bleak for us still when compared to the diverse technology available in more "normalcy climates.
Of course living through the decades since Asimov wrote that story, it seems the aliens have plenty of other reasons to keep our species quarantined.
And then consider that any civilization capable of interstellar travel would already need to be harnessing energies that make nukes look like firecrackers.
https://www.youtube.com/watch?v=rG_Eh0J_4_s
I almost did mechanical engineering, in my placement before starting a degree I didn’t start I was working with detonation guns to fire tungsten carbide into machined parts to make them last far longer in nuclear power stations.
That had finished, just work on jet engine blades.
https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
Plus, a rocket with a nuke on the other end can still destroy a city if you point it in the right direction. There's no such thing as an unarmed spaceship.
Because going to war can benefit you and / or harm your enemies. There's not much to do out in space compared to our home planet.
Just speculation on my part, but I would think the Isp would be higher than the usual chemical combustion regimes due to higher temperature in the detonation volume. Pretty interesting stuff.
Finally spacecraft will be able to produce the characteristic "vvvzzzhzhzh" sound we know from movies like Star Wars. Heard only inside the ship, of course, but likely it will permeate the whole ship while the engine is on.
Sort of like ramjet vs scramjet difference. “I guess that’s better, if you think it can be done, I don’t know though” thing.
This one uses continuously happening detonation along a circular path, and has little to do with those.
(technically I should say "incompressible vs compressible" but you get the imagery)
If it can live up to more efficient, cheaper, and lighter then it will certainly see widespread use.
There are bound to be issues with new larger designs, but nothing show stopping is expected.
Now I don't know how feasible is making a nuke as small as you suggest.
> Project Daedalus later proposed fusion explosives (deuterium or tritium pellets) detonated by electron beam inertial confinement. This is the same principle behind inertial confinement fusion. Theoretically, it could be scaled down to far smaller explosions, and require small shock absorbers.
That's an interesting tidbit about the size. Also reminds me of the Deadalus spaceship from the stargate universe.
But it sounds like politics is the only limit here, surely they can ammend the treaty to allow space-travel work under IAEA supervision.
- massive mess if it goes wrong in any way
- putting nukes in space is banned by treaty and would be an ugly precedent
-Japan has committed to not making nukes and has for obvious historical reasons a difficult relationship with the topic.
(If Japan wanted to become a nuclear power, they relatively easily could for a country that doesn't have any, but that would be a major thing and not a side thing of some science project)
Isn't 155mm 15cm? Close enough I would say if it was an actual fission explosion.
As for safety, nukes in space are safe and you can launch them using conventional propulsion and use nukes only in space and also launch from point nemo or cook islands so you are at least 3000mi away from large populations.
I get these challenges are real but if the advantage over ion propulsion is great then it sounds like they are worth overcoming.
Lessening an absolutist stance on this in favor of a more nuanced regulatory policy that requires more in depth checking seems to me like something we'll regret later when we find the agency is toothless, either because it always was in regards to this or because it was slowly defanged without people noticing.
If something goes wrong during the launch and the rocket explodes, isn't that basically exploding a dirty bomb in the upper atmosphere? Is 3000 miles really enough of a buffer zone?
Since that paragraph is talking about detonation over a populated area, 3k miles away even in the atmosphere I would think wouldn't cause much of an actual harm.
But a solution might be to enrich the radioactive material in a space station in orbit.
As for what might be feasible within the laws of physics, rather than current engineering, I'm not sure there's a clear answer. Increasing the density of the fissile matter reduces its critical mass, which is why they implode the core with conventional explosives in most designs. There are other ways of compressing matter to very high densities. For example, subjecting it to hot enough plasma, like in a magnetic confinement fusion reactor, might work. But stuff like that is science fiction and will be for a long time.